Currently, decanted, dealcoholized mash is frequently used as processing water (in a recycling process) in order to minimize waste water and its disposal. However, dealcoholized mash, also called slop or distiller's wash, contributes acid to the process and causes an increase in the pH. As a rule, the acid is neutralized with a leaching solution, such as brine or lime. A disadvantage of this process is that neutralization produces detrimental salts, i.e. they inhibit the fermentation process.
A consistently stable pH value is an essential factor in alcoholic fermentation. The most favorable value for the main saccharification of sweet mash in steam mashing lies generally in the range 5.3 to 5.7. As a result of the formation of natural acid due to yeast and, at times, due to "false" acid resulting from infection organisms, the pH value decreases during the process of fermentation; normally most pronounced during the fermentation as a result of the yeast growth. The lowest limits of the pH value required for the individual mash types (4.2 to 4.3 or 4.5 to 4.6) can generally be securely maintained during uninterrupted operation. However, should any form of infection occur, primarily due to bacteria introduced from the environment, as is especially possible during recycling, then the acid content, under certain circumstances, will increase dramatically, whereby the pH value will fall below the required level.
An acid increase that is too high also jeopardizes the post saccharification process and thereby the post fermentation products; and also is a disadvantage because sugar or accohol is consumed to form the acid. An execcsivly strong or rapid acid buildup, therefore, has both a direct and an indirect detrimental effect on the yield. An infection, especially by way of certain lactic or butyric acid bacteria, is damaging for the yeast or can even be a strong yeast poison.
In the past it has been recommended to maintain a high pH value in alcohol fermentation with sulfuric or hydrochloric acid, and a low pH value with calcium hydroxide. However, such regulation, by way of acid or base additives, requires a relatively exact dose in order to avoid the respective opposite result. Furthermore, care must be taken with regard to the formation of salts during the continuous exchange from neutralization to acidification.